Alkylation of dialkyl sulfate obtained from an overhead absorption phase

ABSTRACT

Combination process for the alkylation of isoparaffin with olefinic material in the presence of sulfuric acid alkylation catalyst wherein olefin hydrocarbon is reacted with used acid catalyst in an absorption zone producing a lighter overhead phase comprising unreacted hydrocarbon together with a portion of the dialkyl sulfate thus formed, and a heavier acid-alkyl sulfate phase comprising the remainder of the dialkyl sulfate. The dialkyl sulfate content of the heavier phase is extracted with isoparaffin being alkylated and the extract solution is passed to an alkylation reactor. The lighter phase from the absorption zone is reacted with isobutane in a different alkylation reactor, optionally in the presence of an additional quantity of the same type olefin reacted to form the dialkyl sulfate.

United States Patent 1151 3,665,050 McGovern et al. 1 May 23, 1972 541ALKYLATION 0F DIALKYL SULFATE 3,428,705 2/1969 Goldsby 260/683 62OBTAINED FROM AN OVERHEAD 3,462,512 8/1969 Go1dsby.. ...260/683 613,502,742 3/1970 Goldsby v.260/683.6l

Assignee: Stratford Engineering Corporation, Kansas City, Mo.

Filed: Apr. 21, 1969 Appl. No.: 817,535

U.S. Cl ....260/683.62, 260/683.6l Int. Cl 1 ..C07c 3/54 Field of Search..260/683.59, 683.61, 683.62

References Cited UNITED STATES PATENTS Bruner et a1 ..260/683.61 Beavonet a1. ..260/683.6l

gc/e from 3/6 Dru/7; I56

I56 Sec Sarp .jysfem Primary ExaminerDelbert E. Gantz AssistantExaminerG. J. Crasanakis AttorneyScofield, Kokjer, Scofield & LoweABSTRACT Combination process for the alkylation of isoparaffin witholefinic material in the presence of sulfuric acid alkylation catalystwherein olefin hydrocarbon is reacted with used acid catalyst in anabsorption zone producing a lighter overhead phase comprising unreactedhydrocarbon together with a portion of the dialkyl sulfate thus formed,and a heavier acid-alkyl sulfate phase comprising the remainder of thedialkyl sulfate. The dialkyl sulfate content of the heavier phase isextracted with isoparaffin being alkylated and the extract solution ispassed to an alkylation reactor. The lighter phase from the absorptionzone is reacted with isobutane in a different alkylation reactor,optionally in the presence of an additional quantity of the same typeolefin reacted to form the dialkyl sulfate.

2 Claims, 3 Drawing Figures Patented May 23, 1972 Sheets-Sheet vlINVENTOR QQY m r 6 W L JS 3/ wa 1 m fl MJ (M /M 0 Patented May 23, 19723 Sheets-Sheet 2 Patented May 23, 1972 3,665,050

3 Sheets-Sheet 5 ALKYLATION OF DIALKYL SULFATE OBTAINED FROM AN OVERHEADABSORPTION PHASE In H. E. Massa, Ser. No. 495,191 Alkylation of AlkylSulfates," filed Oct. 12, I965, therein is shown methods of andapparatus for absorbing olefins, particularly propylene, into acidstreams from the settler or settlers of an alkylation reaction systemThe absorption process is so operated and manipulated via apparatus andprocess conditions as to produce dialkyl sulfates or dipropyl sulfate(DIPS) which, after removal of catalyst contaminants therefrom arerecycled to the alkylation reaction zone for transformation intoalkylate with the freeing of sulfuric acid. A sufiicient excess ofolefins or propylene is employed in the absorption step that an overheadfrom the absorption stage back to the alkylation reaction zone carriessome DIPS, excess propylene and propane.

The instant invention is concerned primarily with the disposition of theabsorber overhead stream above mentioned, with separate alkylation ofthe DIPS and olefin contained in this stream provided.

To this effect, a separate alkylation reactor from the main alkylationreactor in the system is used to alkylate the DIPS and olefins from line156, which represents the absorber settler overhead. It should be notedthat this stream contains the purest DIPS produced in the absorptionprocess and, because of the requirements for an excess of olefins in theabsorption system, as set out in Massa Ser. No. 495,191, supra, thisstream will also always contain some molecular olefin. Yet further,additional molecular olefin can be added to this stream by by-passing aportion of the propane-propylene feed directly to line 156 (the PP feedto the absorber section) which gives the alkylation reactor systemoperator control over the amount of molecular olefin alkylated with thealkyl sulfate.

Some authorities feel that acid strength has a bearing on the quality ofalkylate produced from pure propylene. They generally feel that a higheracid strength promotes a high quality alkylate. I have, therefore, shownthe DIPS alkylation contactor as providing the highest acid strengthreactor in the alkylation reactor train or system.

Provision is further shown on the drawing for feeding the fresh acidseparately to any contactor in the train. Thus, the acid strength in theDIPS reactor is also subject to independent control. In a specificoperation, with particular product goals the optimum acid strength canbe determined by experiment by the operation for the particular unitinvolved and, thereafter, the strength maintained at the desired value.

Early work in alkylation of propylenes indicated that a higher reactiontemperature was required. Commercial experience has not particularlyconfirmed this theory, but the separate alkylation of DIPS and propylenefrom the absorber system overhead will permit independent temperaturecontrol which can be set for the optimum temperature for the particularplant involved.

The flow diagram of FIG. 2 illustrates a multiple alkylation reactorsystem with series acid flow modified by provision for fresh acid toeach contactor, which permits the establishment of practically anydesired acid strength profile at each contactor.

Basically, the propane-propylene feed from the catalytic cracker orother source will essentially all be fed to the SARP absorption system(FIG. 1). In certain specific cases, however, it may be desirable toadjust the propylene content of the overhead line from the SARPabsorption systems second settler by by-passing fresh propane-propylenefeed directly into this line before said feed gets into the alkylationreactor.

In other cases, where a very large proportion of the total olefin sentto the plant (alkylation and SARP) is propylene, it may be desirable,for balancing the load on the alkylation reactors, to send a portion ofthe propane-propylene feed to the alkylation reactors with thebutane-butene feed,

It should be emphasized that in any case wherein alkyl sulfates arealkylated by isoparaffin, it is necessary that some molecular olefin bepresent in the reactor. The amount of molecular olefin required willdepend upon the specific feed and operating conditions in a givenreactor system and means for adjusting to the optimum are provided.

An object of the instant invention is to improve an alkylation reactionsystem which has a sulfuric acid recovery process associated therewith,by virtue of providing a separate alkylation reactor to handle theoverhead from the absorption system (containing DIPS and propylene, aswell as propane) in a separate alkylation reaction vessel, whereby thepurest DIPS produced in the absorption process and a quantity ofmolecular olefin will be separately alkylated thereby to produce themost optimum alkylate product possible in said separate vessel.

Another object of the invention is to provide an alkylation reactionsystem having a sulfuric acid recovery process as sociated therewithwherein a plurality of other alkylation reactors is associated with analkylation reactor which only alkylates the DIPS and the olefins fromthe overhead of the last settler in the sulfuric acid recoveryabsorption stage.

Another object of the invention is to provide an alkylation reactionsystem having a sulfuric acid recovery process associated therewithutilizing a plurality of alkylation reactors wherein one of thereactors, namely, that receiving the overhead from the SARP absorptionstep second settler, is con trolled and controllable with respect to therelative amount of molecular olefin which is alkylated with the alkylsulfates in said overhead by virtue of bypassing the propane-propylenefeed to the SARP step as desired to the SARP overhead reaction feed.

Another object of the invention is to provide a sulfuric acid recoveryprocess associated with a series of alkylation reactors, wherein one ofsaid reactors receives the overhead from the settler in the SARPabsorption step which has the purest DIPS therein and also somemolecular olefin (as well as additional molecular olefin is desired) andwherein a higher acid strength is or may be provided to said alkylationreactor which has the DIPS and quantity of pure propylene fed thereto.

Another object of the invention is to provide a train of alkylationreactors which have a sulfuric acid recovery process associatedtherewith, wherein means are provided for feeding fresh acid separatelyto any contactor in the train, thereby to subject the acid strength inany reactor which may receive DIPS and free olefin from the absorptionstep of the SARP process to independent control. Thus, in operation, theoptimum acid strength for one or more of the alkylation reactors in thesystem can be determined by experiment for the par ticular unit orsystem involved and the strength thereafter maintained at the desiredvalue for each or every unit.

Another object of the invention is to provide a train of alkylationreaction vessels associated with a sulfuric acid recovery process insuch manner that the overhead from the absorption settler having thepurest DIPS and free propylene therein is passed to one of thesereactors where independent temperature control is available to providethe optimum temperature for the particular reactors and the entire plantinvolved.

Another object of the invention is to provide an improved method foralkylating straight DIPS (dipropyl sulfates) in that additional freepropylene is or may be provided to any or all alkylation reactors in analkylation system which receives DIPS or dialkyl sulfates to alkylate.

Another object of the invention is to provide an alkylation reactionsystem utilizing a SARP process where fresh pure DIPS from the settlerhaving the freshest purest DIPS are alkylated in a separate reactor inan improved manner, this manner including providing a quantity of freepropylene or olefin with said fresh pure DIPS or DAS to such alkylationreactor.

Other and further objects of the invention will appear in the course ofthe following description thereof.

SARP SYSTEM IN FIG. 1

In FIG. 1 is shown an acid recovery system utilizing a two stageabsorption phase with an extraction phase followed by an acid treatmentstep. Absorbers 1 and 2, seen at 140 and 141, are Stratco contactors ofthe type seen in Putney US. Pat. No. 2,979,308, issued Apr. 1 l, 1961,entitled "Apparatus for Controlling Temperature Change, etc." Theextraction phase is preferably carried out in a rotating disc contactingvessel 142 and the acid treatment stage in a contactor of the typepreviously described at 143. Power means 140a, 141a and 143a drive theimpellers in each of the respective contactors with power means 142supplying drive for the RDC. Settling vessels are seen at 144 for thefirst stage absorber, 145 for the second stage absorber and 146 for theacid treater.

A preferably preponderantly propane-propylene feed is then input tocontactor 140 at the first absorption stage through line 147. This ismixed in vessel 140 with the bottoms from the second stage absorbersettler vessel 145 passed therefrom via line 148. The effluent of theNo. 1 absorber is passed to settler 144 through line 146 and comprisesprimarily dialkyl sulfates, namely, dipropyl sulfate, perhaps a smallpercentage of monopropyl sulfates, normal paraffinic hydrocarbons of thepropane level and an excess of olefinic hydrocarbons. No excess acid, ineffect, is found at this stage, sufficient olefin being provided andsufficient mixing efiected in the two absorbers that virtually allsulfuric acid in the input through line 148 to contactor 140 is reacted.There is a quantity of acid soluble polymeric contaminants and water inthe settler 144 contents, as well.

The overhead from settler 144 is taken off through line 149 and passedto contactor 141 (No. 2 absorber) where it is met by an incoming streamof used alkylation acid via line 150. This material has come down intothe acid recovery system via lines 151 and 152 through pump 153. Line152 coming out of the alkylation system is line 137. The effluent fromabsorber No. 2, contactor 141, passes overhead through line 154 tosettler No. 2 at 145. The bottoms from settler No. 1 at 144 are passedthrough line 155 over to the extraction phase of the acid recoverysystem.

To sum up the functional side of the absorption system, the used acidcoming down through lines 137-152 goes into the No. 2 absorber where itmeets the overhead from the No. l settler 144. Thus the originalpropane-propylene feed has already been depleted of a certain amount ofolefin via what has been taken out in the No. 1 absorber. The reactoreffluent from the No. 2 absorber 141 is thus acid rich and propylenepoor. The bottoms from the No. 2 settler 145 have been stripped ofexcess normal propane, other light hydrocarbons and at least a slightexcess of propylene (required to drive the absorption reaction to thedialkyl sulfate state). These light components and some much smallerpercentage of alkyl sulfates dissolved therein are taken off overheadfrom the No. 2 settler through line 156.

Returning to the No. 2 settler, the bottoms therefrom, comprisingacid-rich and propylene-poor absorption product, are passed via line 148to absorber No. 1 at 140 where the already partially sulfated acid ismoved strongly to the dialkyl side by the impact of the newpropane-propylene feed input to the contactor through line 147. Theeffluent through line 146 has a considerable excess of propylene andlight hydrocarbon. The settler 144 contents is stripped of the lattertwo through line 149 which passes to the No. 2 absorber 141. Theultimate absorption product, very preponderantly dialkyl sulfate, butalso including any acid, water and acid soluble contaminants, is takenout line 155.

Indirect heat exchange of the absorption reactor steps at 140 and 141 isprovided by flowing bottom hydrocarbons from flash drum 62 through line138 to take-off lines 157 and 158 connecting to tube bundle headers1401; and 141b, respectively. After a heat exchange connection at 159,line 138a connects into return line 139 to flash drum 62. Return lines1570 and 158a from headers 1401; and 1411) connect into line 138a tocomplete the circuit through the tube bundles of absorbers and 141. Theentire absorber-settler system is maintained under sufficient pressurethat all the reactants of the absorption step are maintained in liquidphase. The pres surization of this system is the reason for pump 153.

The reaction or absorption is exothermic, resulting in a rather highheat release at the point of reaction, thus cooling is required tomaintain the reaction temperature at the desired level of approximately30-40 F. A significant portion of the dialkyl sulfate goes into solutionin the hydrocarbon phase. Thus, after the reaction mix is withdrawn fromthe contactor and separated, a portion of the dialkyl sulfate leaves theseparating vessel with the hydrocarbon phase. In the showing of FIG. 1,the return of the overhead from the No. 2 settler into the alkylationsystem via line 156, is optimal.

Isobutane for extraction of the diisopropyl sulfate from the alkylationsection is supplied through line 122 from fractionation recycle line 114from deisobutanizer 109. After passing heat exchange at 159, this linepasses to rotating disc contactor 142 or other suitable countercurrentflow extraction vessel. The heavy phase from the No. 1 absorber settle,through line and line 162 passes to the other end of the RDC. In theRDC, the heavy phase undergoes continuous countercurrent extraction ofisobutane. The bulk of the dipropyl sulfate, some monopropyl sulfate andtraces of water and conjunct polymers dissolve in the isobutane streamand form the extract which leaves the top of the extractor vessel 142through line 163. The remainder of the heavy phase, comprised of anyunextracted dipropyl sulfate, some monopropyl sulfates, and the bulk ofthe water and acid originally present in the alkylation acid leaves thebottom of the extractor through line 164 and is withdrawn from the unitas spent acid.

The extract from the previous step flows to the acid treater contactor143 through line 163 where it is brought into contact with a relativelyminute amount of alkylation acid pumped from the No. 2 absorber feedstream through line 165. This acid picks up the traces of conjunctpolymers dissolved in the extract. The reaction mix from acid treatercontactor 143 flows via line 166 to settler 146 for phase separation andthe treated extract from the settler 146 is returned to the strongestacid alkylation contactor for alkylation of the dipropyl sulfate andconsequent strong acid release. This return is through line 167. Theheavy phase from the acid treater settler 146 is recycle pumped throughlines 168 and 169 by pump 170 for reextraction of any dipropyl sulfatepicked up with the conjunct polymers.

Refrigeration is required on both absorber contactors and on theisobutane chiller 159. The refrigerant operating temperaturerequirements are typically in the 10 20 F. range. This can be suppliedby the vaporization of hydrocarbon from the flash drum section of theeffluent refrigeration system. Since the bulk of the refrigeration loadis required for heat of reaction which normally is part of totalalkylation reaction heat load, the total refrigeration duty is onlyslightly increased. Some shift in duty and some changes in vapor flowrates are encountered.

High degree of extraction efficiency is necessary for maximum recoveryof propyl sulfates. Whatever dipropyl sulfate is present in theraffinate from this step represents an acid loss from the process. Thisloss should be minimized. A rotating disc contactor as seen in Reman US.Pat. No. 2,601,674, issued June 24, 1952 entitled Liquid ContactApparatus, etc. is here used as the extractor, operating with ahydrocarbon phase continuous. The extractor is designed to operateliquid full at a temperature the same as or slightly below thealkylation reactor temperature. Little or no heat is generated in theextractor, so temperature control may be effected by chilling theisobutane feed stream. The pressure in the extractor and the followingacid treater system is allowed to float with the alkylation reactorpressure.

With respect to the acid treating step, the purpose is to scavengetraces of conjunct polymeric compounds or acid oil from the extract witha small amount of alkylation acid.

At the same time, efficient interfacial contact is required for thenecessary degree of scavenging. A Stratco contactor is used for thisstep, preferably. The heat of solution generated in this step is sosmall compared to the volume of extract that no heat transfer surface isprovided in the contactor. A slight sub-cooling in the extraction stepmay be employed to insure that the treated extract will leave thetreater settler at essentially the alkylation reactor temperature.

The overhead line 156 from settler 145 has a valve thereon which is156a. Prior to valve 156a, alternative No. 2 settler overhead take-offline 300 may be employed. The latter has valve 301 and back pressurevalve 302 thereon whereby the light phase overhead from settler 145 maybe passed altematively through valve control lines 303 and 304 to eitheracid treater 143 or RDC 142.

In the systems contemplated in FIG. 1, utilizing either overhead line156 directly passing settler 145 overhead to the alkylation reactionzone or line 300 passing same to the RDC or acid treater, it iscontemplated that both olefin and alkyl sulfates values in the settler145 overhead would be conserved. These systems emphasize the maximumutilization of acid, but not particularly the total conversion ofpropylene by reaction with acid. Rather, the recovery of propylene bydirect alkylation in the alkylation reaction step is visualized. Also,in the system of FIG. 1 it is contemplated that a richer propylene orolefin feed addition to absorber 140 through line 147 will be utilized,rather than a leaner propylene mixture.

The acid treating step shown in FIG. 1 is optional. In a twostepabsorption section as shown in FIG, 1, where there is relatively littlepropylene overhead from settler 145 to be used in one of the mannersseen in FIG. 1 (e.g., passage to acid treater), the acid treater at 143is less valuable and thus is less attractive.

It is necessary, in any absorption system of a sulfuric acid recoveryprocess that at least certain portions of the overhead from the settlerstage terminating the absorption section (through line 156 in FIG. 1) beretained in the system so that the sulfate values (as well as anyolefinic hydrocarbon in the overhead from settler 145) in the system ofFIG. 1 be retained in the system.

If it is desired that the acid treater stage be omitted from the system,the line 163 from the RDC would run directly into 167, thus returning tothe alkylation reaction zone. Bottoms from the RDC through line 164would still be spent acid.

It is also feasible to utilize a one-stage absorption system, where,necessarily, the absorption phase of the acid recovery system must beoperated olefin-rich whereby there will be a more considerable excess ofolefin in the absorption settler overhead and a lesser percentage-wiseproduction of dialkyl sulfates. In this case, it is most and veryessential that the sulfate and olefins in the overhead from the absorbersettler be conserved in the system.

In the event that the overhead from the absorber settler is from asingle absorber vessel and settler vessel system, it is useful to dividethe absorber settler overhead between a direct recycle to the alkylationreaction zone and a feed to (l) the RDC, (2) the acid treater, or (3)both. In the latter manners, the propylene is maintained in contact withall acid values to minimize the quantity of alkyl sulfates produced andthereby maintain the reaction in the absorption section in the directionof producing dialkyl sulfates or in the direction of the dialkylequillibrium. Likewise, any sulfate values in the absorber settleroverhead are conserved in any one of these variations of the system andare recycled to the alkylation reactor either from the acid treatersettler overhead, if the acid treater is present in such single absorbervessel-settler vessel absorption step in the SARP process, or from theRDC output (equivalent to line 163 in FIG. 1),

Such a single stage absorption system utilizing a rich propylene(paraffin poor) feed to the absorption step may be highly recommendedunder certain circumstances, with the overhead from the singleabsorption settler containing a substantial percentage of unreactedolefin and with a relatively direct passage of same to the alkylationreaction step being desirable. Where a time tank system is utilized,such a single stage absorption apparatus featuring complete recovery ofthe excess olefins and also sulfate values in the light phase from theabsorption step and alkylation and, by virtue of the driving force ofthe high olefin content in the absorption step, the best conditions foracid utilization.

Referring to FIG. 1, the back pressure valves seen in this figure online 156 and connecting line 300 thereto, serve to maintain theillustrated absorber section or absorber contactors and associatedsettlers in said section under such pressure that all flowing materialsin the absorber section are maintained in liquid phase. While it ispossible to produce alkyl sulfates in either liquid or vapor phase,liquid phase operation is much preferred for the maximum production ofthe dialkyl sulfates. In the liquid phase reaction, the absorption ofpropylene is quite rapid and relatively high yields are obtained in arelatively short time. In either phase, efficient contacting, relativelyshort reaction time and isothermal conditions are important for thelatter.

Several variations of conserving valuable materials in the absorptionstep light phase (such as excess olefin if present and alkyl sulfatesdissolved in light hydrocarbons) may be utilized, depending upon theapparatus complex desired. A system as in FIG. 1 which utilizes both amultiple stage absorber section in the SARP section and an acid treaterand a system which utilizes but a single absorption stage in the SARPsection with an acid treater are preferred when the absorber system isoperated with olefin in the absorber system light phase. Whether theabsorption light phase goes directly to alkylation or passes thereto viathe RDC (extractor section) or acid treater in whole or part, the olefinand alkyl sulfate values are conserved in the alkylation reaction zonein all cases. The presence of olefin from the absorber light phase inthe RDC or acid treater affords the maximum exposure of acid values toolefin for reaction to dialkyl sulfate and, additionally, providesthroughout the entire system a driving force to shift the reactionequillibrium toward dialkyl sulfate production.

A contacting device can be provided which accomplishes, in a singlevessel, a countercurrent flow of acid and hydrocarbon feeds andincorporates or provides, by virtue of its design, multiple reactionstages or zones. In essence this is a rotating disc contactor having alower level input line for incoming hydrocarbon with greatest propylenestrength, an upper level input line for used alkylation acid, an upperlevel (above the latter line) outlet for an absorption light phase, andan output line from the vessel below the first described line for outputof a heavy phase which has been maximally converted to dipropyl sulfate.

We have attempted to alkylate propyl sulfates and a mixture of propylsulfates and propylene in a test unit. The unit operation for a limitedperiod and the material balance of 6 hours of operation on a mixture ofpropyl sulfate and propylene are shown on the attached tables.

These data tend to indicate that a straight propyl sulfate will notsuccessfully alkylate and that some fresh olefin is required to properlycontrol the reaction. Thus, while charging straight propyl sulfates, theacid strength continued to decrease. After the addition of propylene tothe alkylation reactor, the acid strength in the system continued toincrease from the low of 87.9 percent at 1:30 a.m. and 3:30 a.m. to ahigh of 90.6 percent at the termination of the run. All during theperiod in question, the quantity of propyl sulfates charged to thealkylation reactor remained constant.

Run N0. 1 acid recovery unit propylene operation 36SD1 Unit log ofoperations 81064 8:10 p.111. Ran out of BB and water entered alkylationreactor. Shut off BB line and continued to feed recycle DIPS from acidrecovery unit to rycle nritl HH.li",, strength. lit-gnu IllIiIlllK RunNo. 1 acid recovery unit 100% propylene operation 36SD1 fresh acid atrate of 2.2 lbs/hr.

of 35 cc./rnin.

3:30 a m Recycle acid strength 87.9%. 5:30 am. Recycle acid strength88.6%. 6:00 a.m. Increased PP feed rate to 67 coymin. 7:00 am. Recycleacid strength 89.1%. 11:30 a.m Recycle acid strength 00.6%. 12:00 noonUnit shutdown.

[Run No. 1Acid recovery unit 1009, propylene operation 36SD11 August 11,1064, 6:00 8.111.I2ZOO noon Alkylation unit balance From acid PP feedIsobutane Total Total recovery direct to to reactor reactor unit,reactor, reactor, feed. cflluent,

Component coimin. cc.-"min. cojmin. ccJmin. ccJmrn.

Alkylation factors:

Temperature, F 50 U0 ratio on reactor feed 8. 8 Percent iCi on totalefiluentu 15.3 Percent diluents on feed (Ci-RC4). 6. 5 Space velocity(50% acid in reactor 0.19 Fresh acid consumption uncorrected forincreasing 1nVen tory strength, lbs. "gallon 0. 48

Alkylate production identification drum #26 octanes F-l Clear 90.6 F2.Clear. F1. Plus3cc 102.8 F-Z Plusdcc.

AST.\I distillation (weathered sample) by Texaco Percent F. Percent 1.

Bar0metric. 735 mm- Referring to FIG. 2, therein is shown an alkylationreaction system utilizing three alkylation reactors (R,, R and R eachhaving a separate settler, (8,, S and 5,). Because of limitations inspace in the drawings, FIG. 2 is shown as coupling with the sulfuricacid recovery system (SARP) of FIG. 1 via a block schematic. FIG. 2 alsocouples with the effluent refrigeration and fractionation systems ofFIG. 3, but, again, because of space limitations in the drawings, thealkylation system of FIG. 2 is shown as a block with respect to FIG. 3and, also in FIG. 3, the SARP system of FIG. 1 is shown as a block.

Referring, then, to FIG. 2, the first alkylation contactor 300 ispowered by motor 301. It also has a cooling tube bundle schematicallyindicated at 302. The feed to contactor 300 comprises, through line 156,the overhead from settler 145 of FIG. 1, namely, propane, propylene andDIPS. The DIPS and propylene are about 50-50, exclusive of propane.Additional propylene to that input through line 156 from the SARP systemmay be inserted from line 303, from the propanepropylene (P-P) feed ofline 147 to the SARP system, line 303 dividing into lines 304 and 305.The additional propylene which may be added as desired to line 156 comesfrom line 304. The isobutane recycle from trap and flash drum 62 vialine 86 is input to vessel 300 via line 306.

Thus, the purest DIPS in the entire system, namely, the overhead DIPSfrom settler 145, excess propylene from the SARP system, additionalpropylene from line 304, as desired and isobutane from line 306 arepassed into the alkylation reactor 300 to be mixed and alkylated in themanner seen and described in the Putney U.S. Pat. No. 2,979,308, issuedApr. 1 l, 1961, for Method and Apparatus for Controlling Temperaturechange Fresh acid is input to the system from line 307 which dividesinto lines 308 and 309. From line 308, which is joined by acid recycleline 310 from the first settler 311, line 312 passes acid to thealkylator 300 whereby the isobutane, olefms and DIPS alkylate in thepresence of the sulfuric acid catalyst. Reaction effluent is taken offfrom alkylator 300 via line 313 and passed to the first settler 311. Theacid phase from settler 311 is removed from the bottom of set tler 311via line 310 and a portion thereof is diverted to reactor 324 via line314. The hydrocarbon phase of the effluent is taken off the top ofsettler 311 through line 315 of reactor 300, the efi'luent from the tubebundle 302 taken off via line 318 to join line 361 (see FIG. 3, center),to pass to trap or flash drum 362.

Thus it is seen that, in the first alkylation reactor 300, the purestDIPS from the SARP system, the overhead propylene from the SARD system,additional propylene, if desired, recyole isobutane and fresh acid, withor without recycle acid from settler 211, are alkylated in reaction 300.Note that fresh acid alone may be used in this particular contactor togive the optimum desired results. Isobutane recycle from fractionationvia line 414 may join line 156.

Referring now to the second alkylation reactor 320, the recycle DIPSstream from either acid treater settler 146 via line 167 or, if an acidtreater is not used, recycle DIPS from the overhead from RDC 142 throughline 163 is passed through line 321 to join line 322 going into reactor320. Reactor 320 is driven by power source 323 and has tube bundle 324served by header 325. The isobutane recycle from trap 362 via line 326may join the DIPS recycle from the SARP unit input through line 322 fromline 326. Likewise, isobutane recycle from fractionation in FIG. 3 vialine 414 may additionally be added to the reactor via line 327 joiningline 328 to the reactor. The butane-butane (BB) feed input to the systemthrough line 116 feeds line 328 via line 329. New isobutane is input toline 1 16 and the alkylation system via line 330. Thus, B-B feed andisobutane go in through line 329 and 328 to reactor 320.

The reaction effluent from reactor 320 is taken off overhead throughline 330 to the second settler 331. Recycle acid from settler 331 is vialine 332 which may join line 314 from settler 311, common line 333taking both recycle acid and stage acid to the reactor 320. Fresh acidvia lines 307, 309 and 3090 may go to reactor 320 via line 333.

The hydrocarbon phase effluent from settler 331 is taken overheadthrough line 334 and passed in effluent refrigeration through backpressure valve 335 to header 325, said hydrocarbon phase, after goingthrough tube bundle 324, passing overhead via line 336 to join commonline 361 to the trap and flash drum.

Referring to the third alkylation reactor 340, this is driven by motor341 and has tube bundle 342 served by header 343. B-B feed and isobutanefrom lines 1 16 and 330, respectively, pass into reactor 340 via line344. This B-B feed and isobutane may be enhanced with isobutane recyclefrom fractionation through line 345 from line 414 out of the top of thedeisobutanizer 109. Isobutane recycle from the trap via line 386, joinedby DIPS from lines 163 or 167 input through line 346 go into the reactorvessel 340 through line 348 to the third settler 349. Recycle acid fromsettler 349 is taken off the bottom thereof via line 350 which passes inrecycle to vessel 340 through line 351 with optional additional acidthrough line 337. The hydrocarbon phase from settler 349 is taken offthrough overhead line 352 and after passing back pressure valve 353 goesthrough tube bundle 342 through header 343 and out overhead line 354.

Lines 354, 336, and 318 join together in a common line 361 which passesto the trap and flash drum 362.

Fresh acid may also be added to contactor 340 via lines 307, 309, 337and 351. A portion of the acid phase from settler 349 is taken to theSARP system through lines 350 and 137.

Referring to FIG. 3, from the upper portion of header line 361 carriesthe hydrocarbon phase effluent, both liquid and vapor, to trap and flashdrum 362. Drum 362 has a divider 363 centrally thereof which divides theliquid inside thereof but permits communication thereover internally ofthe vessel for vapor phases from both sides of the trap.

Vapor overhead from trap 362, comprising light excess isoparafirnichydrocarbons and normal paraffinic hydrocarbons are taken off throughline 364, passing to compressing stage 365 and condenser 366 and thencevia line 367 to accumulator 368. Liquid from accumulator 368 may passthrough line 369 through valve 370 back to trap 362 or, alternatively,bottoms liquid is taken ofi through line 371 via pump 372 through a heatexchange step at 373 to depropanizer tower 374. The overhead from tower374 is taken off through line 375 through cooler 376 and to vessel 377.Overhead from ves sel 377 goes out of the system through line 378 aspropane, with the bottoms returned to tower 374 as reflux via pump 380and line 379. The bottoms fraction from tower 374 are withdrawn throughline 381 through heat exchange at 373 and through cooling step 382 andvalve 383 to the bottoms of trap 362. Reboiling takes place via line 384heated at 385.

The trap and flash drum bottoms on the left hand side of the trap andflash drum in the view are linked with the acid recovery system, but arereturned and handled with respect to the alkylation reaction andassociated systems via line 86, pump 387, valve 388 controlled by levelcontrol 389. Line 386 returns the trap bottoms, largely comprisingunreacted isoparaffinic hydrocarbons, to the three alkylation reactors300, 320 and 340 of FIG. 2.

On the right hand side of barrier 363 in the view, trap bottoms arereturned into the system via line 390 through pump 391 and valve 392controlled by level control 393. From valve 392, the trap bottoms arepassed via line 393 through heat exchange at 394 to meet line 395passing to a caustic wash step at 396 with a receiving vessel at 397.From vessel 397, recycle line 398 splits into line 399 out of the systemand line 400 which, via pump 401, returns the caustic wash bottomsthrough the mixer 396. Fresh caustic is input to the system through line400a. Overhead from the caustic operation passes the alkylate throughline 402 and mixing step 403 after input of fresh water at line 404 tovessel 405. Bottoms from 405 go out of the system at line 406, with theoverhead passed through line 407 and via heating step 408 todeisobutanizer tower 409.

The overhead from tower 409 is taken off through line 410, condensed at411 and passed to vessel 412. Liquid from vessel 412 passes via line 413to the tower as reflux and to fractionation recycle line 414 via cooler415 and heat exchange at 394 to the three alkylation contactors throughline 114 as seen in FIG. 2.

Part of the fractionation recycle may be diverted to the acid recoverysystem through line 122 after cooling at 415, as described for FIG. 1.

Reboiling in the deisobutanizer tower is seen at 423 with heat appliedand 424. Bottoms from the deisobutanizer tower are passed via line 425to debutanizer tower 425a. The overhead from the latter is taken offthrough line 426 through condensing at 427, accumulation at 428 andrecycle for reboiling through line 429 through pump 430. Normal butaneis removed from the system through line 431. Bottoms from debutanizertower 425a go out of the system through line 432 after condensation at433 with reboiling of the lower fraction of the achieved at line 434with heat applied at 435.

We claim:

1. In a combination process wherein olefin is reacted in an absorptionzone with used sulfuric acid alkylation catalyst from an alkylationreaction zone, referred to hereinafter, yielding an absorption zoneoverhead phase comprising unreacted olefin, light parraffin hydrocarbonand a portion of dialkyl sulfate formed in said absorption zone and aheavier acid phase including dialkyl sulfate, said phases are separated,said acid phase is extracted with isoparaffin yielding a dialkylsulfate-isoparaffin extract solution and a raffinate acid, and saiddialkyl sulfate-isoparaffin extract solution is passed to saidalkylation reaction zone, the improvement wherein said overhead phaseand isoparaffin are charged to a separate alkylation reactor whereinsaid charged isoparaffin is alkylated with said dialkyl sulfate in saidoverhead phase.

2. The process of claim 1 wherein olefin hydrocarbon of the same typecomprising the dialkyl sulfate in said overhead phase is charged to saidseparate alkylation reactor.

2. The process of claim 1 wherein olefin hydrocarbon of the same typecomprising the dialkyl sulfate in said overhead phase is charged to saidseparate alkylation reactor.